Encrypted Persistence

Fasq Security provides a specialized persistence layer that ensures your cached data remains encrypted even when the application is closed.

Drift Persistence

The security package includes a DriftPersistenceProvider built on the powerful Drift (formerly Moor) library. It uses a high-performance SQL database (SQLite) for storing query snapshots.

Features

• AES-at-Rest: Every byte written to the disk is encrypted.
• Schema Safety: Fully typed database schema.
• Atomic Updates: Ensures cache consistency even if the app crashes during a write.
• Query Key Support: Efficiently indexes and retrieves data using Fasq’s complex query keys.

Setup

To enable encrypted persistence, you need to configure the persistenceOptions of your QueryClient using the DriftPersistenceProvider.

import 'package:fasq/fasq.dart';
import 'package:fasq_security/fasq_security.dart';
 
void main() async {
  // 1. Initialize security plugin
  final security = DefaultSecurityPlugin();
  await security.initialize();
 
  // 2. Configure persistence
  final persistence = DriftPersistenceProvider(
    // The security plugin provides the encryption key for the DB
    encryptionKey: security.getDatabaseKey(),
  );
 
  final client = QueryClient(
    securityPlugin: security,
    persistenceOptions: PersistenceOptions(
      provider: persistence,
    ),
  );
 
  runApp(QueryClientProvider(client: client, child: MyApp()));
}

How It Works

1. Key Exchange: When the app starts, the SecurityPlugin retrieves the database master key from the platform’s secure storage.
2. Transparent Encryption: As Fasq core attempts to persist a query result, the DriftPersistenceProvider encrypts the payload before it hits the SQLite file.
3. Background Writes: Database operations are performed asynchronously to ensure they don’t block the UI.

Performance Tuning

For applications with very large datasets, you can tune the persistence behavior:

PersistenceOptions(
  provider: persistence,
  // Only persist data if it's been in the cache for at least 1 minute
  minPersistenceAge: Duration(minutes: 1),
  // Ignore small updates to reduce disk I/O
  onPersist: (snapshot) => snapshot.dataSize > 1024,
)

Security Considerations

• Database File: The database file is stored in your app’s local documents directory but remains unreadable without the hardware-protected key.
• Backup: Encrypted databases are typically excluded from cloud backups (auto-backup) by default for security, though this can be configured.

Next Steps

• Security Overview - Return to the overview.
• Caching Strategy - How persistence interacts with cache timing.